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People ask some difficult questions in forums!

I have a couple of other topics in queue for my next articles: The first topic is a summary of some very interesting classes that I could not attend in Auckland, during RTC AUS 2013 (see my previous post about it). So, I am reading the handouts, and then I will publish my comments about those classes. The second topic that is in stand-by is how to model a special chair that Gary Page sent me by email from Auckland. We talked about this chair, face to face, in Auckland, during the RTC conference, so I promise him to study if I could find a way to model that chair in a short time (he said he spent three days). That chair is difficult, and he made it parametric, and with renderings, so I don’t know if I am going to be able to make it yet. So these two will be my future blog articles, soon. Since those two articles are not ready yet, and since it’s already more than two weeks after my previous article, I want to publish today something that I can get done more quickly. So, let me talk about these two recent difficult questions that I have seen in forums.

Difficult question 1 ) “I need that the figure on the top remains parallel to the base”

A user by the username of “Wagurto” posted this question in the Augi forums, and then in Revitforum. The image says: “I need to create a figure like this with these vertices flexible so I can place it where I want. But I need that the figure on top remains parallel to the base. So far I was able to create the base using adaptive components but I am unable to edit the base and keep the top parallel. Any suggestion would be highly appreciated.”

OK, let’s see… Wagurto posted two images to illustrate his question. This is the first image, below. Do you see any adaptive points at the corners? No. Do you see any parameters or dimensions, or reference planes driving the points? No. So I don’t know what exactly Wagurto has done already to solve the problem. I see a solid, which could have been made by making some changes to one of the predefined mass elements from the library, but nothing else…

…and this the second image, explaining that the corners should be flexible and that the interior edges of the roof should remain parallel to the exterior edges of the form.

My solution

I posted this image as a reply to Wagurto‘s post in Revitforum, along with this text:

“If you don’t need this for mass floors and schedules, then, it’s OK to do it with the generic adaptive template, in this way:

  • 4 adaptive points will give you the flexible corners of the form.
  • A couple of diagonals will take care of bisecting the angles.
  • Reference points on the diagonals, (# 1 on the illustration), with a distance along the line, contro11ed by parameter.
  • Reference points on each of the adaptive points, (# 2 on the illustration), contro11ed by an offset, to create the top of the ‘walls’.
  • Reference points on top of the # 1 points, lifted a certain offset, ( # 3 in the illustration) to create the vertices for the flat ‘roof’. ”

Wagurto’s reply

“Thank you Alfredo for your response. However, I think your method will only work in a square or regular quadrilateral. But if the figure is an irregular quadrilateral then it won’t work. Can you send me your Revit family for further analysis? thanks in advance.”My comments:1) The corners have adaptive points, so how come Wagurto says that this “method will only work in a square or regular quadrilateral” ?. This comment makes it difficult for me to believe that Wagurto had really been working on this. If the corners are supposed to be flexible, then we need adaptive points, don’t we?

2) Can I post the Revit family? Well, no, I cannot post the family. Why? Because I don’t have it. All I did was a sketch to give an idea about how to solve this, but it’s just an idea. I had not actually found a method to determine the exact location of the points indicated as # 1 in my illustration. That’s where the real problem is. Also, because, in order to post a family, it needs to be working, correct? and, if the family is going to be working, I would have spent some hours doing it, right?, and if it’s not working, you’re going to say that it’s not working… etc, etc,… (Plus, I had been following that thread in Augi, that “dialog” between Damon.Sidel and Wagurto, and I did not want to fall into the same process… read and judge by yourself).

So I prefer to post an illustration with the idea, and based on that idea you do your own homework. It’s your problem, anyway. I don’t mind sharing an idea in forums, if you do the rest. If you can’t do your part, then, you need to commission someone to do your family, and pay for it. Part of my income is making families, but not for free, of course. This is a difficult family that takes some significant time to figure out and some other significant time to complete, test, and debug.

But Wagurto did not seem interested in doing the rest… see that thread in Revitforum.

Is there a solution to this problem of keeping the interior lines parallel and connected at an intersection?

Yes, I discovered it, later on. There is a way to make parallels to lines that are created with adaptive points, and find the point at which those parallels intersect. Sounds easy, but it is not. The solution I have found is shown in the following image. The distance between two adaptive points can be found by using reporting parameters. Also, we can find the angle between two reference lines, (A); the angle parameter is not reporting, but the value updates when the adaptive points are moved, and it can be used in formulas. The solution to create a parallel is to find the mid point of each reference line in between the adaptive points (p1). Project another point (p2) a certain offset distance (d) , and from that point, project two points, one towards one side (p3), and another one to the opposite side (p4) a distance that is half of the distance between the two adaptive points (known by the reporting parameter). With p3 and p4 I make a new reference line, which is the parallel I need. Then, from the end point that is close to the angle (A), project another point (p-int) back into the reference line, a distance (x) that you can find by Pythagoras‘ formula, since you know the offset (d) and the angle (a) which is half of (A).


The procedure described above needs to be done for each one of the four corners of the family, because each corner is adaptive and may have a unique angle.

As you can see, people ask some difficult questions in forums!
…and some people expect the helper to solve the family and upload it for them. :confused:

Difficult question 2 ) “How to model this pier head?”

This is another difficult question, in my opinion. This object is very difficult to do with precision with the generic model adaptive template, with surfaces. Why? Because it is hard to keep the curves with the correct curvature. The other option is to do it with generic families, making a combination of pieces, as if it was a puzzle, using a combination of solids by different methods, with some very precise (2d) profile families.

This is the AutoCAD drawing that describes the pier head: (it is available for download in Revitforum, at this link).



If you like to play with jigsaw puzzles, maybe this is a good game for you:

  • piece # 1 is an extrusion, for the base of the pier. Make the height parametric, and save it as separate family.
  • piece # 2 is the “arm” of the pier. This is a swept blend solid. Use the curve in the elevation of the AutoCAD drawing as the path.
  • piece # 3 is the first curvature that begins above the joint level. Again, use the curve in the elevation of the AutoCAD drawing as the path.
  • piece # 4 is what remains at the center of the pier after doing the previous pieces, at least the portion that can be done as an extrusion. Use your own Revit file to find the profile for the extrusion.
  • piece # 5 is a separate face-based family, which is made of two profiles, to fill the gaps left by the previous family, and make that curvature. It is a swept blend solid, sloped, and cut by a curved void.

All the pieces from # 2 to # 5 should be assembled as a family, such as “pier_top”, work-plane based. The base should be its own family, such as “pier_base”, with a parameter for the height. Then, in another family, classified as one of the Structural categories, you can bring “pier_base”, and on top of it, put “pier_top”. Assign materials to the families, and there you have the concrete pier, with a parametric base.

Easy? No, certainly not.

My friend Cellophane replied to this question like this:

“You can use a sweep or an extrusion with several voids. Without actually trying it I’m not sure which will work out best.”
…and the original poster, Magicstone1214, replied like this:

“Please teach me more detail. I tried also but can not receive best result. Thank you.


I hope Magicstone1214 meant “please show me…” instead of “please teach me…” Those are two different things. If you have some previous knowledge, you can solve your difficult family by looking at an illustration that shows the idea of the solution, yes. But if you don’t have that previous knowledge, that lack of training cannot be fulfilled in the format of a forum, you need to find some training.

About Wagurto, well, he said that I did not want to go the extra mile. (!) I said that I had already given him 3/4 of a mile but he did not want to walk the last quarter.

People ask some difficult questions in forums!

See you in our next blog…

2013 Planta1.com, inc. , Alfredo Medina | permission to reproduce this article is granted if the name of the author and the URL of this article receive proper credit.


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